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An Improved Subgroup Theorem for HNN Groups with Some Applications
Published online by Cambridge University Press: 20 November 2018
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In [4], a subgroup theorem for HNN groups was established. The theorem was proved by embedding the given HNN group in a free product with amalgamated subgroup and then applying the subgroup theorem of [3]. In this paper we obtain a sharper form of the subgroup theorem of [4] by applying the Reidemeister-Schreier method directly, using an appropriate Schreier system of coset representatives. Specifically, we prove (in Theorem 1) that if H is a subgroup of the HNN group
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- Copyright © Canadian Mathematical Society 1974
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